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Developing a risk-based method for predicting the severity of fire accidents in road tunnels
Published in Chongfu Huang, Zoe Nivolianitou, Risk Analysis Based on Data and Crisis Response Beyond Knowledge, 2019
Panagiotis Ntzeremes*, Konstantinos Kirytopoulos, Vrassidas Leopoulos
Step 1.3 deals with the identification of those parameters included in the aforementioned factors and which influence the fire behavior. Regarding the traffic conditions, there are two parameters that are crucial, the annual average daily traffic expressed in vehicles per hour and the percentage of heavy good vehicles in the traffic volume. The significance of these parameters accounts for their influence on the piston effect. Piston effect refers to the forcedairflow in the tunnel and practically is the only deterring force towardback layering till the mechanical ventilation is fully activated (Ingason et al., 2015). Its importance is particularly significant in case of unfavorable differencesin pressure between the tunnel portals. The magnitude of the piston effect plays a crucial role inwhether the backlayering develops and, if so, in its length. As far as the environmental conditions are concerned, the difference in pressure between tunnel portals and the ambient temperature are identified. The first one due to its influence on the backlayering while the second one affects the air temperature of the tunnel air flow. Since all these parameters are subjected to changes, they should be treated stochastically.
Urban railways and rapid transit systems
Published in Peter White, Public Transport, 2017
As indicated in the previous chapter, for urban systems with frequent stops, this is determined by two main factors: acceleration and overcoming rolling resistance. Aerodynamic resistance is of little importance at the fairly low speeds attained by urban railways, although critical for intercity modes. However, it is a factor in tunnels, where little clearance is provided between train and tunnel, creating a ‘piston’ effect. The need for frequent bursts of high acceleration, owing to close station spacing, may lead to higher energy consumption; high acceleration may itself impose a weight penalty, owing to the higher proportion of motored axles (up to 100 per cent for rates of 1.0 metres/second/second and above) thus required. Kemp (2007) indicates ‘good practice’ of about 0.030 kW/h per seat-km for electric suburban stock.
Kinetics of Rock Breakage by Blasting
Published in M.I. Petrosyan, Rock Breakage by Blasting, 2018
It is well known that a rapid transformation of the explosive in a narrow cavity leads to the initiation of a shock wave which attenuates over distance from the blast site and converts into a stress wave. The cavity expands due to the piston effect of highly compressed gases either immediately after initiation of the shock wave or simultaneous with it. It should be borne in mind that in the breakage of rocks by blasting charges of chemical explosives, no shock wavefront occurs. Hence the shock wave per se is not of specific interest for analysing the mechanical effect of blasting; rather, the stress wave and piston effect of gases are of particular interest from the research point of view.
Three-dimensional numerical simulation of unsteady airflow in high-speed/ultra-high-speed elevator based on multi-region dynamic layering method
Published in Mechanics Based Design of Structures and Machines, 2023
Qing Zhang, Hao Jing, Shuai Qiao, Ruijun Zhang, Lixin Liu
At present, with the development of the elevator to high-speed and ultra-high-speed, aerodynamic problems in the hoistway have gradually appeared, which has a great impact on the ride comfort of elevators. When high-speed/ultra-high-speed elevator is operating at high speeds in a narrow hoistway, due to the limitations of the hoistway, the air in the windward area of the car is compressed and flows forward rapidly. The high-speed airflow in the annular space around the car will be formed in the opposite direction of the car. This phenomenon is called the piston effect. The high-speed airflow violently rubs against the hoistway and car walls, with certain roughness characteristics, and large amounts of aerodynamic noise will form. Yokota, Sugiyama, and Matsukura (1986) showed that the aerodynamic noise produced by an elevator operating at high speeds is much larger than that of mechanical noise. In addition, the unsteady change of the airflow around the car and periodic or quasi-periodic separation of the vortex at the rear of the car will also lead to vortex noise and car vibrations. Scholars abroad the world have established a variety of effective noise reduction measures through the study of the airflow characteristics in tunnels (Zhu, Hu, and Thompson 2018; Hu, Tang, and Zhang 2018; Xiang et al. 2018). Gong (2019) found through calculation and analysis of test data that opening ventilation holes at the side of the hoistway is helpful for reducing the velocity of the piston wind, thus reducing the noise level in the car during elevator operation. In addition, Li, Yu, and Lu (2009) controlled the piston effect using an exhaust and pressure reducing system, a pneumatic smoke shield system, and variable air supply system. Using this approach, the safety of elevator evacuation in high-rise building fires can be effectively improved.